What Determines a Positive Outcome of Spinal Manipulation for Persistent Low Back Pain: Stiffness or Pain Sensitivity? A Randomized Trial

1.0 Background 1.1 Treatment of persistent low back pain Low back pain (LBP) is one of the leading causes of years lived with disability. In Denmark, many patients are treated conservatively in private practice via general practitioner, chiropractor and physiotherapist. It is well known that LBP often is recurrent or chronic condition. Patients with LBP often report pain relief following spinal manipulation although clinical and research findings are mixed . There is clear evidence that spinal manipulation is able to give short term pain relief, increase range of motion and the clinical outcomes are comparable to other common interventions for persistent LBP. Unfortunately, there are no reliable means to determine beforehand whether spinal manipulation is likely to provide pain relief for a given patient and it is common practice to simply try a series of treatments to assess the effect.

1.2 Segmental dysfunctions Spinal manipulation is directed at spinal mechanical dysfunctions. However, reliably identifying mechanically dysfunctional segments has proven difficult. In an attempt to objectively quantify such dysfunctions, a mechanical spinal indentation apparatus,, the VerteTrack (VT) has been developed and when compared to the generally unreliable palpation findings of an experienced clinician, no correlation was found.

Without reliable and objective indicators of the presence of spinal dysfunctions, clinical trials of spinal manipulation are bound to include both patients with and without biomechanical dysfunction, thus potentially obscuring any effect of spinal manipulation in the treatment of such dysfunctions. This heterogeneity in the experimental groups could, at least in part, explain the conflicting evidence.

To address this, a preliminary study has compared quantified spinal stiffness measured by VT and the outcome of spinal manipulation which reported a positive correlation between objectively quantified spinal stiffness and clinical improvement following manipulation in a cohort of acute LBP patients. The study suggests that VT may potentially serve to identify a subgroup of patients with LBP, who also has a higher probability of a positive response to manipulative treatment.

1.3 Factors complicating treatment of persistent low-back pain After the onset of low-back pain, the central neural pathways which conduct, modulate and integrate the pain stimulus changes over time as pain persists and becomes more excitable: It is evident that the nociceptive receptors become hyperexcitable, leading to increased transmission of nociceptive sensory input, which in turn causes central hypersensitive and possibly an attenuation of descending pain-inhibiting mechanisms. Overall, this results in enhanced local pain responses (hyperalgesia) and sometimes widespread increased pain sensitivity (generalized hyperalgesia).